1. Field of the Invention
The present invention relates to a multiple light source type light pipe which can be used to constitute a plane light source unit excellent in light utilizing efficiency and excellent in luminance and uniformity of luminance and to constitute a reflection type or transmission type liquid-crystal display device bright and easy to view, and which can provided as an emission light color change system.
The present application is based on Japanese Patent Application No. Hei. 11-345908, which is incorporated herein by reference.
2. Description of the Related Art
A heretofore known light pipe is a side-lighting type light pipe made of a plate-like member having rough surfaces or white dots in one of the upper and lower surfaces for scattering light incident on the side surfaces of the light pipe to thereby output the scattered light to the other one of the upper and lower surfaces. Such a side-lighting type light pipe is used as follows. That is, a light source is disposed on a side surface of the light pipe to thereby form a plane light source unit. The plane light source unit is combined with a liquid-crystal cell to thereby form a reflection type or transmission type liquid-crystal display device.
There was, however, a problem that the side-lighting type light pipe was inferior in luminance and uniformity of luminance and inferior in display quality. Although there was a proposal to dispose light sources on a plurality of side surfaces in order to improve luminance, it was difficult to eliminate variation in luminance. Incidentally, liquid-crystal display devices are classified into a back-lighting system and a front-lighting system in accordance with the position of arrangement of the plane light source unit relative to a liquid-crystal cell. In the aforementioned scattering system, there was a problem that it was difficult to use the scattering system as a front-lighting system because a display image was disturbed in the scattering system. Such a front-lighting system has been in demand for improvement, so that light emission colors can be changed in the front-lighting system in the same manner as that in the back-lighting system, with the advance of popularization of application of liquid-crystal display devices to portable telephone sets, etc.
An object of the present invention is to develop a light pipe which can be used to constitute a plane light source unit excellent in light utilizing efficiency and excellent in luminance and uniformity of luminance and to constitute a reflection type or transmission type liquid-crystal display device bright and easy to view, and which can be applied also to a front-lighting system so that light emission colors can be changed.
According to an aspect of the present invention, there is provided a light pipe comprising: a plate-like member at least having an upper surface, a lower surface, and side surfaces between the upper and lower surfaces, at lease two of the side surfaces constituting incidence side surfaces extending in left-right and front-rear directions of the plate-like member; and a light output means formed in selected one of the upper and lower surfaces so that incident light incident light to the one of the upper and lower surfaces from each of the incidence side surfaces is made to go out from the other one of the upper and lower surfaces by the light output means, the light output means being constituted by a repetitive structure of prismatic structures having ridgelines extending along each of the incidence side surfaces respectively.
According to another aspect of the present invention, there is provided a plane light source unit comprising the aforementioned light pipe, and light sources disposed on the incidence side surfaces, respectively, of the light pipe.
According to another aspect of the present invention, there is provided a reflection type liquid-crystal display device comprising the aforementioned plane light source unit using a light pipe made of a plate-like member having a light output means in its upper surface, and a reflection layer-including liquid-crystal cell disposed on the lower surface side of the light pipe of the plane light source unit.
According to another aspect of the present invention, there is provided a transmission type liquid-crystal display device comprising the aforementioned plane light source unit using a light pipe made of a plate-like member having a light output means in its upper or lower surface, a transmission type liquid-crystal cell disposed on the upper surface side of the light pipe of the light source unit, and a light reflection means disposed on the lower surface side of the light pipe.
According to the present invention, light from a light source is made to be incident on at least two side surfaces of a light pipe so that the incident light is made to exit from one and the same surface through a light output means constituted by a repetitive structure of prismatic structures. Hence, the light from the light source can be converted efficiently to form a plane light source, and a plane light source unit excellent in luminance and uniformity of luminance can be obtained. When the plane light source unit is used as a back-lighting or front-lighting system, a reflection type or transmission type liquid-crystal display device bright and easy to view can be formed. Further, a liquid-crystal display device using a front-lighting or back-lighting system, in which light emission colors can be changed according to the combination of different-color emission light sources can be also formed.